Happened while flipping through a 400-page PDF file. The LED associated
with the capacitive button went solid green, disabling the entire row of
buttons. Happened once for the lower row, and once for the right side row.
With the lower row frozen, tried turning it off with the stylus. Could not turn
it back on with the middle button. Resetting always works, and the stylus
menus also work. Version 1.6 of firmware. Help/comments appreciated.

1st, make sure you are not using a wall charger. Several will cause this type of behavior. If that is not the problem, does it occur with other PDF documents. Sometimes when turning to a page with a figure with lots and lots of data, the device will appear to hang. It eventually displays the page.

Did you also have a blinking red LED on top when the lower green one froze? The blinking red would mean that an error occurred. At that point, a specific combination of green LEDs come on to tell iRex what the error was.

I've had the same situation a few weeks ago. It was possible to work with the stylus. So no problem, but after finishing work and shutting down the device, the (full) battery was empty over night. No recharging was possible. After a reset all works fine again.
Conlusion: if the capacitive buttons fail - make a reset at once for saving the battery.

Nope - I don't have a wall charger, and the red LED didn't come on. The document
is not very complex, and normally loads and can be read fast. The capacitive sensor
LEDs were definitely hung. I could not get the box to power-up after a power-off, when
the bottom row got frozen. That could not be from PDF slowness. Since the stylus
menus worked, this is an annoyance than a major bug.

i have the same problem . and the top LED is flashing Orange , after 1.6 upgrade.
but i have done a work around , i have disabled the LEDs altogether , and use only the working set of LEDs .
any ideas where is the problem?

Happened while flipping through a 400-page PDF file. The LED associated
with the capacitive button went solid green, disabling the entire row of
buttons. Happened once for the lower row, and once for the right side row.
With the lower row frozen, tried turning it off with the stylus. Could not turn
it back on with the middle button. Resetting always works, and the stylus
menus also work. Version 1.6 of firmware. Help/comments appreciated.

well i have never tried to find out the effect of environment on it , but certainly , it's an interesting theory. also , it could not be the built quality or anything like that , but it's weird since when i complained to iRex , they just quickly suggested for DR to visit them back in their factory , if it's not a known problem , they might never fix it.